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tank/hv earth electrode and nearby concrete pad with mounted lighting column

psychicwarrior
Hello - good day to all !


Any experience/experiences that might provide a few tips/watch out fors etc, most gratefully received.


Contemplating the run of buried SWA cabled over 100m for outdoor lighting (and electric gates) passing by a pole mounted transformer, where it's been confirmed by the distributor that there is a Tank/HV earth electrode setup  at the pole. Whilst explaining this was not a rigid rule (more a guide and just as well as it shuts off the only feasible route), it was suggested best [in this case] to stay out of a 9m radius if burying cables - but the situation would be helped if this had to be compromised, by running the cabling in ducting/conduit when in the ground.


What are opinions on the siting of concrete pads with threaded rod to secure [conductive] column lighting in this context; this would seem a more serious concern within the 9m advice, is it a no-no, is there anything that can be done to mitigate (aside to using all non-conducting materials), or is it a non-issue (I feel not) ? 


I have no experience of such a long distance, but any tips and advice on pulling SWA along duct for over 100m would be uiseful too :-)   \\m/


Thank you all

Habs

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  • 0
    In practise most of our TNS and TNC-S supplies will have many varied contacts with earth over a very large area I would think

    Indeed - but hopefully none of them within the HV area of a 'hot' transformer site - the DNOs are usually very careful about that.


    Actually I've been thinking about the little TT islands again and I'm not sure now it's a good idea. During a HV fault the ground (and hence the TT island's LV earthing system) goes up to some considerable voltage (perhaps several thousands of volts) - yet the L & N lines remained referenced to normal LV earth which hopefully is well outside the HV areas and so remains close to true earth potential. The insulation between L&N and c.p.c/exposed-conductive-parts is then stressed by the HV fault voltage which is probably well outside what the LV insulation can withstand - so we should perhaps expect insulation failure, so not good.


       - Andy.
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  • 0
    In practise most of our TNS and TNC-S supplies will have many varied contacts with earth over a very large area I would think

    Indeed - but hopefully none of them within the HV area of a 'hot' transformer site - the DNOs are usually very careful about that.


    Actually I've been thinking about the little TT islands again and I'm not sure now it's a good idea. During a HV fault the ground (and hence the TT island's LV earthing system) goes up to some considerable voltage (perhaps several thousands of volts) - yet the L & N lines remained referenced to normal LV earth which hopefully is well outside the HV areas and so remains close to true earth potential. The insulation between L&N and c.p.c/exposed-conductive-parts is then stressed by the HV fault voltage which is probably well outside what the LV insulation can withstand - so we should perhaps expect insulation failure, so not good.


       - Andy.
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